Maximum pipe diameter through a compartment wall or floor
40 mm
Nominal internal diameter for a non-fire-rated pipe; larger pipes need a tested sleeve, collar or non-combustible material
Every figure for this topic is on one page: Cavity barriers and fire stopping around openings and services
Read the full answerWhere a plastic pipe passes through a fire-separating element without a proprietary collar, its size is limited so the opening cannot become a large breach.
Basis in regulation
How to check it on site
Check the pipe type and diameter at every separating wall or floor crossing, and log the collar product where one is used.
Common failure
Full-bore 110 mm soil pipes taken through a compartment floor with expanding foam only.
Effective from 22 August 2026. Last updated 23 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.